As shown in FIG. 1, in a mobile communication system of the W-CDMA (Wideband-Code Division Multiple Access) scheme, a receiving apparatus (a mobile station, for example) performs despreading processing on a W-CDMA signal transmitted by a base station, and calculates downlink radio quality using an obtained common pilot channel (CPICH). The calculation of the downlink radio quality may include obtaining received power of a desired wave and an interference wave.
For example, in the mobile communication system of the W-CDMA scheme, the receiving apparatus calculates received power in the downlink by performing averaging processing on received signals rn and rn+1 of two pilot signals Sn and Sn+1 continuously transmitted in a time axis direction using the following equations.
                              λ          1                =                              1            /            2                    ⁢                      N            s                    ×                                    ∑              1                              Ns                -                1                                      ⁢                                                                                                r                    n                                    +                                      r                                          n                      +                      1                                                                                                  2                                                          (        1        )                                          λ          2                =                              1            /            2                    ⁢                      N            s                    ×                                    ∑              1                              Ns                -                1                                      ⁢                                                                                                r                    n                                    -                                      r                                          n                      +                      1                                                                                                  2                                                          (        2        )                                RSCP        =                              1            /            2                    ×                                                                λ                1                            -                              λ                2                                                                                    (        3        )                                ISSI        =                  λ          2                                    (        4        )            In the equations, RSCP (Received signal code Power) indicates received power of a desired signal, and ISSI (Interference Signal Strength Indicator) indicates received power of an interference signal. Also, rn=αSn+In and rn+1=βSn+1+In+1 hold true, wherein α and β indicate amplitude variation and phase variation that are effects of fading for the transmission symbols respectively, and In and In+1 indicate interference wave component including thermal noise of the symbols respectively.
In the mobile communication system of the W-CDMA scheme, two pilot symbols continuously transmitted on the time axis using a single frequency are used for calculating received power in the downlink.
In a time period during which channel variation between two pilot symbols is small, propagation paths can be regarded as almost the same propagation path. Thus, coefficients α and β of variation of propagation paths by which Sn and Sn+1 are multiplied respectively can be regarded to be almost the same, so that received power of the desired signal and the interference signal can be estimated accurately. That is, when rn and rn+1 can be regarded to be almost the same, λ1 represents components in which the desired signal component and the interference signal component of the two symbols are added, and λ2 represents only interference components of two symbols. Thus, the desired signal component can be obtained by |λ1−λ2|/2.
However, as shown in FIG. 2, the mobile communication system of the LTE (Long Term Evolution) scheme is configured such that pilot symbols are mapped on the time axis and the frequency axis discontinuously, and transmitted. In the mobile communication system of the LTE scheme, the pilot symbol may be called a reference signal (RS). Therefore, in the case in which the propagation path is estimated using two pilot symbols, if delay path and moving time are large, propagation paths between two pilot symbols cannot be regarded as the same propagation path. That is, α and β cannot be regarded to be the same, so that correlation between received signals (rn and rn+1) becomes small. Thus, in the equation (2), the interference signal component cannot be extracted, so that received power of the desired signal power cannot be estimated accurately.